This invention relates to a fast breeder reactor system capable of supplying a thermal/electrical output corresponding to the required scale. More particularly, the invention relates to an autonomous, decentralized fast breeder reactor system suited also to an underground site.
Owing to the basic characterizing feature of a fast breeder reactor, namely the fact that fast neutrons are used in production of fission energy and in the breeding of fuel, the breeder has a dense core. Accordingly, in a larger scale power reactor, it is necessary to take a change in core reactivity into consideration in order to accumulate a larger volume of fuel within the core. In this connection, an inherent safety mechanism peculiar to fast breeder reactors is required. For example, since reactivity is controlled so as to be negative by a Doppler change or the like, core safety is maintained at a high level. However, in order to assure the reliability of these mechanisms, design limitations are imposed upon the core structure and control, etc. For example, a flat core structure, a structure which allows core expansion, or control for leveling core neutron flux is necessary. These limitations will not be solved merely by reducing the size of the core. There is a need to realize a universally applicable optimum nuclear reactor system in which rationalization of design is achieved based on a harmonious balance between safety and economy.